Having a very strong understanding of music theory, and specifically harmony, is incredibly useful when creating music that uses vertical chord structures and how the pitches of each chord move to the next chord i.e. voice leading - smooth voice leading - avoiding parallel 5ths, direct 5ths, taking advantage of common tones between chords, keep chord tone members mostly moving by small intervals (2nds, 3rds) etc. etc.
Having said that, rules are great for learning, developing fluency in - and then forgetting. Theyre useful devices.
Also, rarely (if ever) did mozart or beethoven or any other composer of the baroque, classical or romantic era ever have 20 layers happening simultaneously. Mozart and Beethoven were actually well known for their economy of sound. Its worth noting that the standard orchestral scores of these time periods only had 13 to 17 unique instruments - often with different groups or sections working in tandem. For instance, all 4 string subsections might create a collective chord movement, like a synth "pad", this would be 1 layer. The same could be said for the brass or w.w.s - or a combination of instruments from different sections to create a more complex timbre - still one layer tho. Probably wouldnt hear more than 4 or 5 layers Tops. On rare occasions a few more.
BUT! If you wanna hear some insane works with amazing orchestration and heavy layering listen to Berlioz (Fantastique) or Dubussy (Le Mer) or Ravel (Daphnis et Chloe). If you wanna hear an orchestra layering 20 unique parts at the same time you gotta go find some crazy 20th/21st century post modern shit i dont even know about - but i assure you it exists . . . maybe George Antheil
. . . education can be a drag, im haunted by it.
Keep it up
Cheers
